Landfill compactors are machines which move over landfill deposits to compact the trash. Compacting the trash maximizes the use of the landfill. When the trash is compacted, more material can be disposed in the landfill because it is deposited more densely. Compacting the trash also helps to ensure long term structural stability of the landfill when it is filled and capped with soil. Similarly, soil compactors are machines which move over soil, gravel, or other materials to compact the material in preparation for road construction or other construction purposes.
Landfill compactors and soil compactors typically feature large, heavy steel wheels. The bodies of the machines are also heavy, and the combined weight of the body and the set of wheels on each machine provides the necessary downward force for compaction. To increase the compactive capability, compactor wheels have often been fitted with tips to concentrate the weight force. This is especially common on landfill compactors, where the tips help compact the trash by breaking and grinding it into smaller pieces. The tips are mounted on the cylindrical, ground facing surface of the wheels which is often formed by a wheel wrapper, a relatively thick section of plate steel that is bent around and welded to the wheel hub. The tips extend radially outward from the wheel wrapper in a direction away from the center rotational axis of the wheel.
Many different landfill compactor tips have been developed for use on compactor wheels. One example of a compactor tip is disclosed in U.S. Pat. No. 3,891,341, issued Jun. 24, 1975, and has a generally square base with a work face having a “dog-bone” outline with larger dimensions extending axially of the wheel. Another example of a compactor tip provided by U.S. Pat. No. 4,074,942, issued Feb. 21, 1978, has a cross-shaped tip portion with tapered or concave surfaces extending downwardly to a generally rectangular body portion. U.K. Patent Appl. Publ. GB 2 214 878, published on Sep. 13, 1989, teaches a generally flat plate-like paddle mounted on a compactor wheel and supported on one side by a wedge or gusset. In a further example, U.S. Pat. No. 5,358,355, issued Oct. 25, 1994, teaches a cleat having sides sloping downward from a cutting face towards a bottom face, and generally toward opposite ends of the cleat, to produce a generally inverted wedge or V-shaped appearance of the cleat. As another example, U.S. Pat. No. 6,619,883, issued Sep. 16, 2003, provides a compactor tooth having a ground engaging surface with a “plus-” symbol profile that increases in cross-section in the forward and rearward directions as the tooth extends from the tip downward toward a mounting block.
As discussed above, these and other compactor wheel tips are provided to improve the compaction of the trash and the soil over which the compactor machines are driven. Compaction is important in the landfill environment because a landfill has a finite amount of space available, so the more densely the trash can be compacted, the more efficiently the space is used, and the more profitable the landfill as a going concern. Consequently, optimizing the compaction achieved by a wheel tip is a consideration for those skilled in the art when designing wheel tips. Closely related to the issue of compaction is the concept of “fluffing.” Fluffing is the tendency of a particular wheel tip or wheel tip assembly to pull the material back up as the tip is exiting the surface of the compacted material, and thereby undoing a certain amount of compaction that was achieved by the tip. Fluffing may be caused by material sticking to the tip and being pulled up as the wheel rotates away from the surface. Fluffing may also occur where edges of the tip engage the material as the tip rotates out of the hole in the surface. The smallest amount of fluffing may be undesirable.
The traction provided by the wheel tips is also a factor considered by those skilled in the art when designing the tips. Traction is important because it allows the machine to move through the trash and to perform the task of compacting the trash or the soil. Traction is more perceivable by the operator of the machines than compaction, but both factors are important in the design of the tip. Traction causing the wheels to propel the machine forward over the surface with minimal slippage is of primary concern. Additionally, traction against lateral slippage, such as can occur when the machine is on the side-slope of a hill, is also an important consideration in compactor wheel tip design.
Packing refers to the adherence of material to the tips and the wheel as the compactor machine passes over the surface. As material packs on the wheel, just as when mud cakes on a shoe, the traction provided by the tips degrades and slippage of the wheels increases. Additional torque may be required to be applied to the wheels due to the added weight of the packed material. Some compactors are equipped with cleaner fingers to remove packed material between the tips, but not all can be removed. Consequently, minimizing the amount of material packing occurring to the wheels is a further consideration of the person skilled in the art performing compactor wheel tip design.
The surfaces over which the compactor machines travel includes abrasive materials that wear away the metal of the compactor wheel tip over time. Materials such as sand and rock may be harder than the metal from which the tips are fabricated, and the friction of the abrasive material removes metal from the tip. The wear rate is not uniform at all points on the compactor tip, so the ground engaging surface of the tip is reshaped over tip as more metal is removed from, for example, the lateral edges of the tips. It is desirable to have compactor tips designed to provide extended though not unlimited useful lives over which the tips provide an acceptable combination of traction and compaction, even as the abrasive materials wear away the metal of the compactor tips and reshape the ground engaging surface.
Several different attachment methods have been used to attach tips to compactor wheels. Welding tips to a compactor wheel is common. Mechanical retention systems have also been employed. For example, U.S. Pat. No. 6,619,883, issued on Sep. 16, 2003, discloses mechanically retaining a landfill compactor tip on a compactor wheel. As another example, U.S. Pat. No. 6,095,717, issued Aug. 1, 2000, discloses a different type of mechanical retention system. Mechanical retention systems, while permitting easy replacement of the tips after they are worn or damaged, can suffer from several disadvantages such as failure of the retention mechanism causing the tip to fall off, looseness of the connection causing movement of the tip leading to collection of debris between the tip and wheel, excessive wear, excessive vibration and noise, and increased frequency of failure.
Welding tips to compactor wheels is still an attractive option as an alternative to mechanical retention systems. However, welding also suffers disadvantages, such as the difficulty of producing a tip from steel with the most desirable metallurgy for durability and wear resistance, while still permitting a consistent, strong, and durable weld joint to be formed between the tip and the wheel. Highly durable and wear resistant steels are desirable in the landfill and soil compacting environments, but tips made from durable steels, such as high carbon and high alloy steels, are most often not easy to weld to the surface of the compactor wheel. Moreover, welding is further complicated where the compactor wheel and the tip are made from different steels. At the very least, creating a consistent, strong, and durable weld joint between a compactor tip and a compactor wheel made from dissimilar metals requires conditions that are difficult to create in the field where this welding often occurs, and may require skilled, experienced welders.
To avoid the difficulty of welding certain types of steels and of welding dissimilar steels, some manufacturers have avoided using highly durable and wear resistant steels. Rather, these manufacturers have used low carbon steels and relied on heat treating techniques to achieve the necessary hardness in the tip. But the need for heat treating appears to have also led to the tips being designed with a geometry that facilitates such heat treatments, but which is less than optimal for compacting. Another alternative manufacturing concept for facilitating attachment of tips to compactor wheels provided in U.S. Pat. Appl. Publ. No. 2009/0045669, published on Feb. 19, 2009, includes a compactor tip assembly having a base and tip that are formed from dissimilar materials. The tip may be formed from high carbon steel for wear resistance, while the base may be formed from low carbon steel for easy welding. The compactor tip assembly is attached to the wheel by welding the base to the wheel after the tip has been welded to the base, possibly at the factory where the conditions can be precisely controlled and repeated for a consistent, durable and strong weld joint as opposed to welding out in the field at the location of the compactor where conditions are less controllable. Even with such a two-piece construction, balancing factors such as durability, wear, traction, compaction, packing, fluffing and the like is important in developing the geometry of the compactor wheel tip.
For these reasons, a need exists for a new technology for compactor wheel tips that may balance these trade-offs to provide a compactor wheel tip that is durable and wear resistant, and provides an acceptable level of traction and compaction for the compactor wheel during the compaction wheel tip's useful life. A further need exists for providing a compactor wheel tip that is both durable and wear resistant, and easily weldable to a compactor wheel.